A method and system for fast simulation of typical fault transient waveform of offshore wind power

Abstract

The application discloses a kind of offshore wind power typical fault transient waveform fast simulation method and system, it is related to offshore wind turbine grid connection and power grid fault simulation technical field, including: obtaining the original typical fault voltage transient waveform at offshore wind turbine grid connection point;Wavelet analysis method is used to the fault voltage transient waveform is filtered and handled, and approximate signal and detail signal are obtained by decomposition, fundamental wave and main oscillation waveform in detail signal are extracted, RLC second-order fault simulation circuit is established, and reconstruction waveform is formed by waveform superposition, reconstruction waveform analytical expression is obtained, the fault transient characteristic parameter required to be solved is determined;The initial value of characteristic parameter is initially fitted, and the final value of characteristic parameter is iteratively solved using nonlinear least square method;Equivalent line parameter value is solved by fitting using fault characteristic expression;It is substituted into fault simulation circuit, and recurrence waveform is generated by simulation simulation.The application can quickly and accurately reproduce offshore wind power typical fault transient waveform.

Description

Technical Field

[0001] This invention relates to the field of offshore wind turbine grid connection and grid fault simulation technology, and in particular to a method and system for rapid simulation of transient waveforms of typical offshore wind power faults. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid development of the offshore wind power industry, the grid adaptability and fault ride-through capability of wind turbines have become crucial for ensuring the safe and stable operation of the power system. As a core device for testing the grid-connected performance of wind turbines, the grid fault simulation device simulates various grid faults by outputting controllable voltage waveforms, accurately and effectively testing the grid adaptability of wind power generation systems.

[0004] Traditional power grid fault simulation devices mostly employ impedance voltage divider fault ride-through testing devices, such as... Figure 1 As shown, the short-circuit impedance is adjusted by switches CB1 and CB2 respectively. and boost resistors and capacitors (or and The switching of the wind turbine generators on and off is used to control the voltage at the grid connection point. The control of voltage rise and fall. However, this test method / device cannot reflect the transient response process of the wind power transmission system to voltage rise or fall changes. Therefore, a grid fault simulation device is needed to generate more accurate fault waveforms to improve the grid connection test of wind turbine units.

[0005] Therefore, the following two types of power grid simulation devices are currently commonly used for fault simulation:

[0006] One approach involves combining a power grid simulation device with a Real-Time Digital Simulator (RTDS). The RTDS simulates the fault waveform, while the power grid simulation device acts as a power amplifier to achieve grid-machine interaction. However, this method has certain drawbacks. Wind power transmission systems are complex, with numerous scenario settings, and the power grid simulation device has limited capabilities, weak high-frequency real-time interaction capabilities, and difficulty in simulating transient high-frequency waveforms during faults.

[0007] Secondly, faults can be simulated quickly and easily in the device controller. By calculating the equivalent impedance of the line between the fault point and the point of common coupling (PCC) voltage, various types of faults in different transmission systems can be equated to the PCC voltage. Combined with the equivalent impedance of the line from the PCC to the generator terminal, the impact of the unit feedback current on the grid connection point voltage can be reflected. However, due to the complex form of the generator terminal voltage and the variable system equivalent impedance in the multi-collection and transmission scenario of offshore wind power, there is currently a lack of a unified and effective equivalent simulation method to reproduce the typical fault waveform characteristics, making it difficult for the grid simulator to generate voltage waveforms with offshore operating characteristics. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, this invention provides a method and system for rapidly simulating transient waveforms of typical offshore wind power faults. By embedding a simplified model into the controller of the grid simulation device, the transient waveforms of typical offshore wind power faults can be reproduced quickly and accurately, meeting the accuracy and efficiency requirements of offshore wind turbine grid connection testing. This solves the problem that existing technologies cannot quickly and accurately reproduce transient responses and simulate transient waveforms of typical offshore wind power faults.

[0009] In one aspect, the present invention provides a method for rapid simulation of transient waveforms of typical faults in offshore wind power.

[0010] A method for rapid simulation of transient waveforms of typical faults in offshore wind power includes:

[0011] Obtain the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine;

[0012] Wavelet analysis is used to filter the transient waveform of the fault voltage, decompose it into approximate signal and detail signal, extract the fundamental wave and main oscillation waveform from the detail signal, establish a second-order RLC fault simulation circuit, and form a reconstructed waveform by waveform superposition, obtain the analytical expression of the reconstructed waveform, and determine the fault transient characteristic parameters to be solved.

[0013] Initial values ​​of the feature parameters are initially fitted, and then the final values ​​of the feature parameters are obtained by iteratively solving the nonlinear least squares method.

[0014] Based on the final values ​​of the characteristic parameters and the fault characteristic expression, the equivalent line parameter values ​​are fitted and solved.

[0015] Substitute the equivalent line parameter values ​​into the second-order RLC fault simulation circuit to generate a reproduced waveform through simulation.

[0016] Secondly, the present invention provides a rapid simulation system for transient waveforms of typical faults in offshore wind power.

[0017] A rapid simulation system for transient waveforms of typical faults in offshore wind power includes:

[0018] The fault transient waveform acquisition module is used to acquire the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine.

[0019] The fault transient characteristic parameter determination module is used to filter the fault voltage transient waveform using wavelet analysis, decompose it into approximate and detail signals, extract the fundamental and main oscillation waveforms from the detail signals, establish a second-order RLC fault simulation circuit, and form a reconstructed waveform by waveform superposition to obtain the analytical expression of the reconstructed waveform and determine the fault transient characteristic parameters to be solved.

[0020] The feature parameter solving module is used to initially fit the initial values ​​of the feature parameters, and then uses the nonlinear least squares method to iteratively solve for the final values ​​of the feature parameters.

[0021] The equivalent line parameter solving module is used to fit and solve the equivalent line parameter values ​​based on the final values ​​of the characteristic parameters and the fault characteristic expression.

[0022] The fault transient waveform simulation module is used to substitute equivalent line parameter values ​​into the RLC second-order fault simulation circuit to simulate and generate reproducible waveforms.

[0023] Thirdly, the present invention also provides an electronic device, comprising: a memory for storing executable instructions; and a processor for executing the executable instructions stored in the memory to implement the above-mentioned method for rapid simulation of transient waveforms of typical offshore wind power faults.

[0024] Fourthly, the present invention also provides a computer-readable storage medium storing executable instructions for causing a processor to execute the executable instructions to implement the above-mentioned method for rapid simulation of transient waveforms of typical faults in offshore wind power.

[0025] Fifthly, the present invention also provides a computer program product comprising executable instructions stored in a computer-readable storage medium; wherein, when the processor of the electronic device reads the executable instructions from the computer-readable storage medium and executes the executable instructions, the above-mentioned method for rapid simulation of transient waveforms of typical offshore wind power faults is implemented.

[0026] The above one or more technical solutions have the following beneficial effects:

[0027] 1. This invention proposes a method and system for rapid simulation of transient waveforms of typical faults in offshore wind power. Based on the controller structure of a power grid simulation device, an embedded simplified equivalent model is constructed to rapidly simulate typical fault scenarios and transient waveforms. In this invention, wavelet decomposition is first used to analyze the transient waveform of the fault voltage waveform at the grid connection point of the wind turbine. Based on the analysis results, a second-order RLC fault simulation circuit is established, and the corresponding fault waveform analytical expression is constructed to determine the required characteristic parameters. Then, the initial values ​​of the characteristic quantities are solved using fast Fourier decomposition, cubic spline interpolation, and exponential fitting to obtain the initial values ​​of the transient attenuation coefficient, transient oscillation frequency, transient voltage amplitude, and waveform phase. Next, a fitting function model is constructed, and the characteristic quantities of the fault voltage waveform are obtained using nonlinear least squares method. The simulation circuit parameters are further calculated based on the characteristic quantity expressions. Finally, the solved circuit parameters are substituted back into the fault simulation circuit, and the simulation is compared to reproduce the waveform fitting degree. The results show that the fault waveform fitting degree reproduced by this method is relatively accurate and can be applied to the rapid fault waveform simulation of a power grid simulator.

[0028] 2. In this invention, the main oscillation waveform is extracted by wavelet decomposition and combined with RLC second-order circuit modeling to effectively reproduce the core features of the fault transient, namely the fundamental wave + main oscillation. The reconstructed waveform has a similarity of more than 90% with the original waveform, achieving high-precision simulation. Moreover, the nonlinear least squares method is used to fit the feature parameters, and the peak value and main frequency errors are controlled within the set range, meeting the accuracy requirements of grid-connected testing.

[0029] 3. In this invention, considering the limitations of the power grid simulation device controller's computing power, the high-order circuit is simplified to a second-order RLC circuit. Combined with the optimization of the initial values ​​of the fault transient characteristic parameters based on FFT + cubic spline interpolation + exponential fitting, the nonlinear least squares method is used to further accurately solve the parameter values, which can reduce the iterative complexity of nonlinear fitting, achieve rapid simulation, and adapt to real-time testing scenarios. By reflecting the characteristics of the submarine cable transmission line through equivalent line parameters, the simulation results can reflect the influence of different line lengths on the fault waveform, and the testing environment is closer to the actual operating conditions of offshore wind power.

[0030] 4. This invention can be directly applied to the embedded model of the power grid simulation device without relying on RTDS high-frequency interaction, and has been verified on the ground test platform of offshore wind turbine. It is suitable for fault ride-through tests in various offshore wind power collection and transmission scenarios and has wide applicability.

[0031] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0033] Figure 1 This is a schematic diagram of a traditional impedance voltage divider fault ride-through test device; where (a) is a schematic diagram of a low-voltage fault generation device and (b) is a schematic diagram of a high-voltage fault generation device.

[0034] Figure 2 This is a schematic diagram of the topology of an existing power grid simulation device;

[0035] Figure 3 This is a flowchart illustrating the rapid simulation method for transient waveforms of typical faults in offshore wind power according to an embodiment of the present invention.

[0036] Figure 4 The wavelet decomposition results and their spectrograms of transient waveforms in this embodiment of the invention are shown.

[0037] Figure 5 This is a schematic diagram comparing the original waveform and the reconstructed waveform in an embodiment of the present invention;

[0038] Figure 6 This is a topology diagram of the second-order RLC fault waveform simulation circuit constructed in an embodiment of the present invention;

[0039] Figure 7 The amplitude-frequency diagram and phase spectrum after FFT calculation in this embodiment of the invention;

[0040] Figure 8 This is a schematic diagram of the envelope curve on the sinusoidal decaying oscillation waveform in an embodiment of the present invention;

[0041] Figure 9 This is a schematic diagram of the fitting curve for obtaining the initial value of the feature quantity by exponential fitting in an embodiment of the present invention;

[0042] Figure 10 This is a comparison diagram of the original waveform and the reproduced waveform when no wind turbine is connected in an embodiment of the present invention;

[0043] Figure 11 This is a comparison diagram of the original waveform and the reproduced waveform when the wind turbine is connected in an embodiment of the present invention;

[0044] Figure 12 This is a simplified equivalent circuit diagram of the wind power AC transmission system in an embodiment of the present invention;

[0045] Figure 13 This is a simplified model simulation verification comparison diagram in an embodiment of the present invention;

[0046] Figure 14This is a schematic diagram of the fault characteristic quantities defined in the embodiments of the present invention; wherein, (a) is the transient attenuation characteristic quantity, and (b) is the transient voltage peak value. Detailed Implementation

[0047] It should be noted that the following detailed descriptions are exemplary and are intended only to describe specific embodiments and to provide further explanation of the invention, and are not intended to limit the scope of exemplary embodiments of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] Example 1

[0049] To achieve rapid and accurate simulation of typical fault transient waveforms of offshore wind turbines, this embodiment employs an impedance RLC equivalent circuit and a controlled voltage source oscillation simulation method, such as... Figure 2 As shown, a fault simulation device is introduced into the power grid simulation device. Considering the computing power limitations of the power grid simulation device controller, a simplified circuit is used as the fault simulation device to reproduce the typical fault waveform. Based on this, an RLC circuit is used to simulate the equivalent impedance of the connection system and generate a fault voltage waveform at the grid connection point PCC. The actual unit is then connected for testing, making the test environment closer to the real scenario of offshore wind power grid connection, thereby quickly and accurately reproducing the typical fault waveform.

[0050] The rapid simulation method for typical fault transient waveforms in offshore wind power proposed in this embodiment is as follows: Figure 3 As shown, the specific steps include:

[0051] Step S1: Obtain the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine.

[0052] Specifically, to simulate faults by embedding a fault model within the fault simulation device controller, a simplified circuit is needed to reproduce the typical fault waveform. Since overvoltage poses a more serious threat to wind turbines, this embodiment focuses on the reproduction of transient overvoltage waveforms. Therefore, in step S1, the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine is first obtained as a prerequisite for the subsequent fault transient waveform reproduction steps.

[0053] Step S2: The fault voltage transient waveform is filtered using wavelet analysis to decompose it into approximate and detail signals. The fundamental and main oscillation waveforms in the detail signals are extracted, and a second-order RLC fault simulation circuit is established. The reconstructed waveform is formed by waveform superposition, and the analytical expression of the reconstructed waveform is obtained to determine the fault transient characteristic parameters to be solved.

[0054] Specifically, considering the computational limitations of the fault simulation device controller, it is difficult to completely reproduce each oscillation waveform of the fault transient process. Therefore, in this embodiment, the original fault transient waveform is filtered to reduce the original high-order circuit to the range that the power grid simulation device can compute.

[0055] Step S2.1: The transient fault waveform is first filtered and pre-analyzed using wavelet decomposition to obtain the waveform proportions of each frequency. For example... Figure 4 The decomposition results shown indicate that each fault waveform can be composed of the approximate signal and detail signal of the next layer. When filtering reaches the last layer, i.e. Figure 5 In the fourth layer shown, approximate signal 4 can almost be considered a 50Hz sine wave, and detail signal 4 contains an oscillating waveform that accounts for the largest proportion besides the fundamental wave. This oscillating waveform is referred to as the main oscillating waveform, and its frequency is called the dominant oscillation frequency. The dominant oscillating waveform accounts for more than 95% of the signal. After superimposing the fundamental wave of detail signal 4 with the dominant oscillating waveform of the dominant frequency, the resulting combined reconstructed waveform is as follows: Figure 5 As shown, the reconstructed waveform has a similarity of over 90% to the original waveform. Therefore, when considering the waveform reproduction simulation, the remaining higher frequencies, which account for a smaller proportion, can be ignored, and the oscillation waveform of the main frequency can be considered primarily. Thus, the expression for the voltage waveform to be reproduced is:

[0056] (1)

[0057] In the above formula, U i This represents the transient voltage amplitude. α i The attenuation coefficient is... β i Angular frequency, θ i The initial phase angle, t Indicates time.

[0058] Step S2.2: Considering that a second-order circuit can generate a combined fault transient voltage waveform of a fundamental frequency and a main frequency at the grid connection point of the unit during fault transients, this embodiment establishes a second-order RLC fault simulation circuit to approximate the fault waveform, which is then connected to the test unit device.

[0059] Specifically, such as Figure 6 As shown, the submarine cable transmission line is equivalent to an RLC circuit. The fault voltage in the power grid simulator is simulated by the direct drop in power supply voltage, thereby establishing a second-order circuit. u s This is the grid voltage. R eq ,L eq , C eq The equivalent line parameters are (equivalent resistance, equivalent inductance, and equivalent capacitance, respectively), and the DUT (Device Under Test) is the device under test, which in this embodiment is the offshore wind turbine to be tested.

[0060] This embodiment ultimately aims to achieve waveform simulation, with the actual goal of calculating the line waveform. R eq , L eq , C eq Equivalent parameters are obtained, and then the calculated equivalent parameters of the line are substituted into the simulation model for waveform simulation and experimental comparison. Before obtaining the equivalent parameters, relevant waveform characteristic parameters need to be extracted based on the waveform characteristics. Existing technologies often decompose the waveform into the fundamental wave and a series of higher harmonic components using discrete Fourier transform. However, this method is essentially a steady-state waveform analysis method and cannot meet the needs of transient waveform analysis. Therefore, this embodiment uses a nonlinear least squares optimization method to fit and evaluate the waveform characteristic quantities. Using this nonlinear least squares method for power system transient waveform analysis has high initial value calculation accuracy, fewer iterations, and high convergence speed for all optimization calculations, thus meeting the needs of transient waveform analysis and optimizing computational efficiency.

[0061] Furthermore, before fitting the line parameters using the nonlinear least squares method, it is first necessary to fit the magnitudes of the fault transient characteristic parameters. However, the nonlinear least squares method is quite sensitive to the selection of initial values; different initial values ​​yield significantly different identification results. Therefore, before performing parameter identification, it is necessary to calculate more accurate initial values ​​for parameter iteration, i.e.:

[0062] Step S3: Initially fit the initial values ​​of the feature parameters, and then use the nonlinear least squares method to iteratively solve for the final values ​​of the feature parameters.

[0063] Specifically, based on the analysis in step S2, the differential equations describing the transient process of the power system can be transformed into a system of first-order linear differential equations. The solution is the current or voltage of the power system fault transient, which can be expressed as the sum of a set of attenuated AC components of different frequencies, as shown in equation (2):

[0064] (2)

[0065] In the above formula, U i This represents the transient voltage amplitude. α i The attenuation coefficient is... β iAngular frequency, θ i Let N be the initial phase angle, and let N represent the total number of harmonic AC components of different frequencies during the transient process of the power system. If the transient process includes 1 fundamental frequency component and 2 harmonic components, then N=2.

[0066] That is, the transient characteristic parameters of a fault include transient voltage amplitude, attenuation coefficient, angular frequency, and initial phase angle. The methods for obtaining the initial values ​​of each characteristic quantity include:

[0067] Step S3.1, angular frequency β i (0) and initial phase angle θ i (0) Selection and solution.

[0068] In this embodiment, the Fast Fourier Decomposition method is first used to perform spectral analysis on the reconstructed waveform to obtain the amplitude spectrum and phase spectrum of the reconstructed waveform. Specifically:

[0069] Discretizing equation (2) yields:

[0070] (3)

[0071] The formula for the Discrete Fourier Transform (DFT) is:

[0072] (4)

[0073] in, M The total number of samples in the discrete signal. n = 0, 1, 2,..., M-1 .

[0074] Furthermore, substituting equation (3) into equation (4) yields:

[0075] (5)

[0076] After calculation using the Fast Fourier Transform (FFT) method, each result component corresponds to a specific frequency component. For the first frequency component in the FFT result... k Each component has a corresponding actual angular frequency and phase:

[0077] (6)

[0078] (7)

[0079] in, F sLet F[k] be the sampling frequency, Re(F[k]) be the real part of F[k], and Im(F[k]) be the imaginary part of F[k]. The corresponding amplitude and phase spectra can then be obtained, as follows: Figure 7 As shown.

[0080] Secondly, based on the amplitude and phase spectra, different amplitudes and phases corresponding to different frequencies can be obtained. According to the sorting of amplitude peaks in the spectrum (i.e., amplitude spectrum), the frequency corresponding to the largest amplitude peak is selected as the main frequency, and the main frequency component is obtained. Then, combined with the phase spectrum, the corresponding phase is determined, thereby obtaining the initial values ​​of angular frequency and initial phase angle in the characteristic parameters. β i (0) and θ i (0) .

[0081] Step S3.2, Transient voltage amplitude U i (0) and attenuation coefficient α i (0) Selection and solution.

[0082] In this embodiment, firstly, for any component of the transient voltage (i.e., any harmonic other than the fundamental wave), i The local maxima of the oscillating waveform (≠0) are fitted using cubic spline interpolation to obtain the envelope curve, where the cubic spline interpolation function satisfies the condition that the first derivative is 0 at the local maximum point.

[0083] Specifically, one component of the transient waveform can be randomly selected as follows:

[0084] (8)

[0085] And order:

[0086] (9)

[0087] but This is the upper envelope signal of the detailed waveform.

[0088] Furthermore, based on the extracted components mentioned above... For signal u t ( t ), for signals u t ( t All local maxima points can be fitted using cubic spline interpolation. .remember u t ( t )exist ttj The first derivative at is m j , j = 1, 2, …, n , n To determine the number of local maxima, cubic spline interpolation is used for fitting. y ( t ), let [ tt 1, tt j The cubic spline function on ] is s ( t ),and s ' ( t j ) = m j ,but s ( t In subinterval The above should satisfy the conditions. s ( tt j-1 ) = yy j-1 , s ( tt j ) = y j ; s ' ( tt j-1 ) = m j-1 ; s ' ( tt j ) = m j The cubic interpolation polynomial is then s ( t )exist[ tt j-1 , tt j The expression on ] is:

[0089] (10)

[0090] in, h j = tt j – tt j-1 .because u t ( t )exist tt jIt obtains a local maximum at that point, therefore we have m j = 0, then we have:

[0091] (11)

[0092] in, t ∈[ tt j-1 , tt j The upper envelope curve. y ( t ) = s ( t ),like Figure 8 As shown.

[0093] Secondly, in obtaining the upper envelope y ( t After that, the envelope curve is fitted using an exponential curve fitting method (i.e., an exponential function) to obtain the initial values ​​of the transient voltage amplitude and attenuation coefficient. U i (0) and α i (0) The fitted curve is as follows Figure 9 As shown.

[0094] Step S3.3: Use the nonlinear least squares method to iteratively solve for the final values ​​of the characteristic parameters.

[0095] In this embodiment, the differential equations describing the transient process of the power system are transformed into a system of first-order linear differential equations. The solution can be expressed as the sum of a set of attenuated AC components of different frequencies. Based on this, the numerical calculation result f in the transient process of the power system is obtained. k It can be viewed as a function f(t) at discrete time point t k Approximate value on ( k = 0, 1, …, n Therefore, a nonlinear least squares fitting algorithm can be used to obtain the provided... n + 1 pair of data points (t) k , f k ) to determine 4 in equation (2) N +4 feature parameters.

[0096] Specifically, firstly, taking the transient characteristic parameters of the fault as the parameters to be solved, let... X = ( x 1, x 2, … , x m ) T The above groups of parameters represent Ui , α i , β i , θ i The vector formed m = 4 N + 4), Construct the objective function as:

[0097] (12)

[0098] Then, determine the parameters. x i ( i = 0, 1, …, m The problem is equivalent to the problem of a given set of conditions. n + 1 pair of data points (t) k , f k ()( k = 0, 1, …, m ; n ≥ m Make the objective function P The problem of finding the minimum value.

[0099] Secondly, using the initial values ​​of the pre-fitted feature parameters as input, and minimizing the objective function as the goal, a nonlinear least squares method is used for iterative solution until the correction error of the feature vector reaches a set threshold, thus obtaining the final fault transient feature parameter values. This includes:

[0100] Set parameters X The initial approximation is X (0) and its truth value X with initial value X (0) The difference is denoted as Δ X (0) ,Right now:

[0101] (13)

[0102] f(t) k , X) in X (0) Expand according to Taylor series and ignore Δ X (0) From quadratic terms and terms of degree higher than quadratic, we get:

[0103] (14)

[0104] In the above formula,

[0105] ;

[0106] Substitute equation (13) into equation (2), and let ,but:

[0107] (15)

[0108] Furthermore, equation (14) can be further written as a modified equation of the following form:

[0109] (16)

[0110] In the above formula,

[0111] ;

[0112] Equation (15) is a m A system of linear algebraic equations of order 1 can be solved by matrix decomposition using the Cholesky method, yielding Δ. X (0) Use this value to correct the initial value. X (0) A new approximation can be obtained. X (1) for:

[0113] (17)

[0114] If the correction error does not meet the predetermined accuracy requirement, i.e. Then utilize X (1) replace X (0) Reconstruct and solve the corrected equation; iterate the above process repeatedly until... Until then, finally obtained X (1) This is the desired final result.

[0115] Step S4: Based on the final values ​​of the characteristic parameters and the fault characteristic expression, fit and solve for the equivalent line parameter values.

[0116] After calculating the parameter values ​​of the fault transient characteristic quantities through the above steps, the line RLC parameters (i.e., equivalent line parameters) are fitted and solved according to the fault characteristic expression that characterizes the mapping relationship between the fault transient characteristic parameters and the equivalent line parameters. In order to eliminate the influence of the unit response on the fault waveform characteristics, the system's wind turbines are replaced by equivalent loads. Simulations are performed under different 220 kV transmission line lengths to obtain the original data of the required fitted waveform.

[0117] As one implementation method, the construction process for the above fault characteristic expression is as follows:

[0118] First, by analyzing and calculating the symmetrical fault situation in the AC transmission scenario of offshore wind turbines, we preliminarily analyzed the factors affecting the transient voltage of the fault at the grid connection point of the wind turbine and constructed a simplified circuit model of the offshore wind power transmission system.

[0119] Specifically, the biggest difference between offshore and onshore wind power lies in the type of transmission lines. The capacitance of the submarine cables used for offshore wind power transmission is much greater than that of the overhead lines used for onshore wind power transmission. Therefore, the influence of transmission line parameters needs to be carefully considered during the simplified calculation of the transmission system. Based on this, a simplified model of the offshore wind power system is established, such as... Figure 12 As shown, where, u PCC The voltage at the wind turbine's grid connection point is represented by an infinite power supply in the model. u s To represent the onshore power grid, a step change in the voltage source is used to simplify the simulation of voltage fluctuations after a system fault. Since the initial fault calculation focuses on the impact of the power grid system on the grid connection point voltage and temporarily disregards the wind turbine's response, the complex dynamic response within the turbine is ignored in this model to reduce the order of the mathematical model and obtain an analytical solution. Norton's principle is used to equate the wind turbine to a current source. i w and parallel impedance Z w In order to further reduce the order of the mathematical model, the transmission line adopts an L-type equivalent circuit. R eq , L eq , C eq These represent the resistor, inductor, and capacitor in the equivalent simplified circuit, respectively.

[0120] Secondly, based on the simplified equivalent model established above, an analytical model of the AC transmission system is constructed.

[0121] Specifically, based on the simplified equivalent model established above, the basic differential equation shown in equation (18) is derived from Kirchhoff's voltage theorem and the node current relationship:

[0122] (18)

[0123] In the above formula, Equivalent inductance Voltage drop at both ends AC power supply voltage, The amplitude of the AC power supply voltage. and These are its angular frequency and initial phase, respectively.

[0124] Solving the above set of differential equations yields the transient voltage expression at the wind turbine grid connection point after a three-phase symmetrical short-circuit fault occurs in the power grid system, as shown in equation (19) below:

[0125] (19)

[0126] in,

[0127] ;

[0128] In the above formula, K 1. K 2. K 3. K 4. C 1. C 2 is the calculated constant. α Indicates the transient decay rate. β This is the transient oscillation frequency.

[0129] make:

[0130] (20)

[0131] (twenty one)

[0132] The expression then simplifies to:

[0133] (twenty two)

[0134] In the above formula, U T This represents the amplitude of the fault transient voltage. U S This represents the steady-state voltage amplitude during the fault. The first part of the equation represents the transient component of the unit's grid connection point voltage, and the second part represents the steady-state component of the unit's grid connection point voltage. The expressions for the time of fault occurrence and after fault clearance are the same. Since overvoltage has a significant impact on the unit and is often closely related to fault transients, we focus on the transient component of the unit's grid connection point voltage after fault clearance.

[0135] Preferably, an equivalent simplified model is built on the PSCAD / EMTDC platform for verification, such as... Figure 13 As shown, the simulation results are basically consistent with the analytical theoretical results.

[0136] Subsequently, based on the analytical model of the aforementioned AC transmission system, fault characteristic quantities (i.e., fault transient characteristic parameters) and their influencing factors are extracted.

[0137] Specifically, observing the voltage waveform at the grid connection point of the wind power transmission system after a fault, the fault waveform mainly includes various transient components. The transient components are mainly affected by transient decay rate, transient oscillation frequency, and transient voltage peak value. These fault characteristic quantities are selected as the focus of research. According to the above analytical expressions, the fault transient characteristic quantities are as follows: Figure 14 As shown, its expression is:

[0138] (twenty three)

[0139] (twenty four)

[0140] (25)

[0141] (26)

[0142] in, α It indicates the transient decay rate, specifically how quickly the voltage at the wind turbine's grid connection point returns to stability after a grid fault is resolved; β This indicates the transient oscillation frequency, specifically the frequency of transient voltage fluctuations at the wind turbine grid connection point after a grid fault is resolved. U Tm It represents the peak value of transient attenuation, specifically the maximum peak value of the voltage component fluctuation at the wind turbine grid connection point after the grid fault is restored. U max This indicates the peak value of the transient voltage, specifically the peak value of the voltage waveform during the recovery process after the fault is cleared.

[0143] Furthermore, by simultaneously solving equations (21), (23), and (24), the fault characteristic expression can be obtained as follows:

[0144] (27)

[0145] In the above formula, x 1. x 2. x 3 represents the equivalent line parameters. R eq , L eq , C eq , Z w For parallel impedance, AC power supply voltage, The amplitude of the AC power supply voltage. ω is the angular frequency.

[0146] In the fault characteristic expression obtained above, the final values ​​of the calculated characteristic parameters are substituted into the expression, namely the final values ​​of transient voltage amplitude, attenuation coefficient, and angular frequency. , , (The initial phase angle may not be reflected in the fault characteristic expression) to fit and solve for the equivalent line parameter values. In this embodiment, the nonlinear least squares method is used to fit and calculate the value of equation (27). Preferably, according to the above algorithm, a fault transient voltage waveform analysis program is written in Matlab, and the correspondence between the obtained line parameters and characteristic parameters is shown in Table 1 below (similarly, the initial phase angle may not be considered in Table 1 below).

[0147] Table 1. Fitting results of line parameters and characteristic parameters

[0148]

[0149] Based on the fitting parameters above, it can be seen that the decay rate and oscillation frequency of the waveform decrease with the increase of the simulated line length, while the peak value of the high-frequency component reaches its maximum when the line length reaches a certain value (40 km in this case), and then gradually decreases.

[0150] Step S5: Substitute the equivalent line parameter values ​​into the RLC second-order fault simulation circuit to generate a reproduced waveform through simulation.

[0151] Specifically, the simplified second-order circuit parameters for different line lengths calculated above are substituted into the simulation model built by PSCAD / EMTDC, and the resulting waveform is called the reproduced waveform, which is the simulated waveform.

[0152] As one implementation method, after simulating and generating the reproduced waveform, the goodness of fit between the reproduced waveform and the original waveform is verified. Specifically, the voltage waveform simulated by the unsimplified model is called the original waveform; the waveform after filtering, containing only the fundamental wave and the main oscillation wave components, is called the approximate waveform; and the waveform constructed from the characteristic parameters fitted by the nonlinear least squares method is called the fitted waveform. Comparison images of these four waveforms at different line lengths are shown below. Figure 10 As shown, the horizontal axis represents time t in seconds (s), and the vertical axis represents per-unit voltage u.

[0153] The characteristic parameters and errors of the simulated waveform and the original waveform when the line is not connected to the wind turbine are shown in Tables 2, 3 and 4 below.

[0154] Table 2. Peak values ​​and errors of simulated waveforms without wind turbine connection.

[0155]

[0156] Table 3. Main frequency and error of simulated waveform oscillation without wind turbine connection.

[0157]

[0158] Table 4. Simulated waveform attenuation rate and error without wind turbine connection.

[0159]

[0160] in, , , .

[0161] When the system is not connected to the wind turbine, the fitting error of the peak value, the attenuation rate, and the oscillation frequency of the fitted waveform are all within the set range (e.g., 10%), and the accuracy meets the requirements. At this time, the influence characteristics of the submarine cable on the fault waveform can be reproduced, and it can then be applied to the power grid simulator.

[0162] Preferably, if the error between the reconstructed waveform and the original waveform is too large after obtaining the reconstructed waveform, it may be due to the large fault harmonics, which cause the loss of a lot of information when using wavelet decomposition during pre-analysis. This can be solved by reselecting the original signal segment with smaller fault harmonics for pre-analysis. Alternatively, it may be due to the sensitivity of the nonlinear least squares method to the initial value, which will converge to a local minimum. Therefore, the choice of the initial value will also affect the characteristic quantity of the reconstructed waveform. This can be solved by selecting multiple different initial values ​​for least squares fitting.

[0163] Furthermore, the fault simulation circuit was connected to the wind turbine to verify whether the influence of the wind turbine response on the fault waveform at the grid connection point was consistent with the original line. The characteristic parameters and errors of the simulated waveform and the original waveform when the line was connected to the wind turbine are shown in Tables 5, 6, and 7. The simulation comparison images are shown below. Figure 11 As shown.

[0164] Table 5. Peak values ​​and errors of simulated waveforms when the wind turbine is connected.

[0165]

[0166] Table 6. Simulated waveform oscillation frequency and error when connected to a wind turbine.

[0167]

[0168] Table 7 Simulated waveform attenuation rate and error when connected to a wind turbine

[0169]

[0170] in, , , .

[0171] The peak value and oscillation frequency errors of the waveforms obtained by fitting using the nonlinear least squares method are within 5% to 7%, and the accuracy meets the requirements. However, the fitting error of the attenuation rate is relatively large. Overall, it can reproduce the influence characteristics of submarine cable on fault waveforms well, and can be applied to power grid simulators.

[0172] Example 2

[0173] This embodiment provides a rapid simulation system for transient waveforms of typical faults in offshore wind power, including:

[0174] The fault transient waveform acquisition module is used to acquire the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine.

[0175] The fault transient characteristic parameter determination module is used to filter the fault voltage transient waveform using wavelet analysis, decompose it into approximate and detail signals, extract the fundamental and main oscillation waveforms from the detail signals, establish a second-order RLC fault simulation circuit, and form a reconstructed waveform by waveform superposition to obtain the analytical expression of the reconstructed waveform and determine the fault transient characteristic parameters to be solved.

[0176] The feature parameter solving module is used to initially fit the initial values ​​of the feature parameters, and then uses the nonlinear least squares method to iteratively solve for the final values ​​of the feature parameters.

[0177] The equivalent line parameter solving module is used to fit and solve the equivalent line parameter values ​​based on the final values ​​of the characteristic parameters and the fault characteristic expression.

[0178] The fault transient waveform simulation module is used to substitute equivalent line parameter values ​​into the RLC second-order fault simulation circuit to simulate and generate reproducible waveforms.

[0179] Example 3

[0180] This embodiment provides an electronic device, including: a memory for storing executable instructions; and a processor for executing the executable instructions stored in the memory to implement the method provided in this embodiment.

[0181] Example 4

[0182] This embodiment also provides a computer-readable storage medium storing executable instructions, which, when executed by a processor, will cause the processor to execute the method described above in this embodiment.

[0183] Example 5

[0184] This embodiment provides a computer program product including executable instructions, which are computer instructions; the executable instructions are stored in a computer-readable storage medium. When the processor of an electronic device reads the executable instructions from the computer-readable storage medium and executes the executable instructions, the electronic device performs the method described in this embodiment.

[0185] The steps and methods involved in Embodiments 2 to 5 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0186] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0187] The above description is only a preferred embodiment of the present invention. Although the specific implementation of the present invention has been described in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for rapid simulation of transient waveforms of typical faults in offshore wind power, characterized in that, include: Obtain the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine; Wavelet analysis is used to filter the transient waveform of the fault voltage, decompose it into approximate signal and detail signal, extract the fundamental wave and main oscillation waveform from the detail signal, establish a second-order RLC fault simulation circuit, and form a reconstructed waveform by waveform superposition, obtain the analytical expression of the reconstructed waveform, and determine the fault transient characteristic parameters to be solved. Initial values ​​of the feature parameters are initially fitted, and then the final values ​​of the feature parameters are obtained by iteratively solving the nonlinear least squares method. Based on the final values ​​of the characteristic parameters and the fault characteristic expression, the equivalent line parameter values ​​are fitted and solved. Substitute the equivalent line parameter values ​​into the second-order RLC fault simulation circuit to generate a reproducible waveform through simulation. The fault transient characteristic parameters include transient voltage amplitude, attenuation coefficient, angular frequency, and initial phase angle; The solution for the angular frequency and the initial value of the initial phase angle includes: The reconstructed waveform was subjected to spectral analysis using the Fast Fourier Decomposition method to obtain its amplitude and phase spectra. Based on the amplitude spectrum and phase spectrum, different amplitudes and phases corresponding to different frequencies are obtained. The main frequency components are determined according to the magnitude of the amplitude peaks in the amplitude spectrum, and the corresponding phases are determined in combination with the phase spectrum, thereby obtaining the initial values ​​of the angular frequency and the initial phase angle. The solution for the transient voltage amplitude and attenuation coefficient includes: For the local maxima of any component oscillation waveform in the transient voltage, the envelope curve is obtained by fitting using cubic spline interpolation; the cubic spline interpolation function satisfies the condition that the first derivative is 0 at the local maximum point; The envelope curve is fitted with an exponential function to obtain the initial values ​​of the transient voltage amplitude and attenuation coefficient. The final values ​​of the characteristic parameters are obtained by iteratively solving using the nonlinear least squares method, including: Using the transient characteristic parameters of the fault as the parameters to be solved, the objective function is constructed as follows: ； In the above formula, X = ( x 1, x 2, … , x m ) T This represents the feature vector composed of fault transient characteristic parameters. m = 4 N + 4. Fault transient characteristic parameters include: To reconstruct the analytical expression of the waveform in discrete time The calculated value, Discrete time The original waveform sample value; The initial values ​​of the preliminary fitted feature parameters are used as input, and the objective function is minimized. The nonlinear least squares method is used to iteratively solve the problem until the correction error of the feature vector reaches the set threshold, and the final fault transient feature parameter values ​​are obtained. The fault characteristic expression characterizes the mapping relationship between the fault transient characteristic parameters and the equivalent line parameters, expressed as: ； The equivalent circuit parameters include equivalent resistance, equivalent inductance, and equivalent capacitance. x 1. x 2. x 3 represents the equivalent resistance in the equivalent circuit parameters. R eq Equivalent inductance L eq and equivalent capacitance L eq , Z w For parallel impedance, AC power supply voltage, The amplitude of the AC power supply voltage. Angular frequency, α For transient decay rate, β This is the transient oscillation frequency.

2. The method for rapid simulation of transient waveforms of typical faults in offshore wind power as described in claim 1, characterized in that, Also includes: After generating the reproduced waveform through simulation, the goodness of fit between the reproduced waveform and the original waveform is verified. The verification process involves comparing the characteristic parameters of the simulated waveforms with the original waveforms when the RLC second-order fault simulation circuit is connected and when it is not connected to the offshore wind turbine. If the errors in waveform peak value, decay rate, and oscillation frequency are all within the set range, then it is determined that the fitting requirements are met.

3. A rapid simulation system for transient waveforms of typical faults in offshore wind power, characterized in that, The method for rapid simulation of transient waveforms of typical faults in offshore wind power as described in any one of claims 1-2 includes: The fault transient waveform acquisition module is used to acquire the original typical fault voltage transient waveform at the grid connection point of the offshore wind turbine. The fault transient characteristic parameter determination module is used to filter the fault voltage transient waveform using wavelet analysis, decompose it into approximate and detail signals, extract the fundamental and main oscillation waveforms from the detail signals, establish a second-order RLC fault simulation circuit, and form a reconstructed waveform by waveform superposition to obtain the analytical expression of the reconstructed waveform and determine the fault transient characteristic parameters to be solved. The feature parameter solving module is used to initially fit the initial values ​​of the feature parameters, and then uses the nonlinear least squares method to iteratively solve for the final values ​​of the feature parameters. The equivalent line parameter solving module is used to fit and solve the equivalent line parameter values ​​based on the final values ​​of the characteristic parameters and the fault characteristic expression. The fault transient waveform simulation module is used to substitute equivalent line parameter values ​​into the RLC second-order fault simulation circuit to simulate and generate reproducible waveforms.

4. An electronic device, characterized in that, include: Memory, used to store executable instructions; The processor, when executing executable instructions stored in the memory, implements the rapid simulation method for transient waveforms of typical faults in offshore wind power as described in any one of claims 1-2.

5. A computer-readable storage medium, characterized in that, The device stores executable instructions that, when executed by a processor, implement the rapid simulation method for transient waveforms of typical faults in offshore wind power as described in any one of claims 1-2.

6. A computer program product, characterized in that, The computer program product includes executable instructions stored in a computer-readable storage medium; When the processor of the electronic device reads the executable instructions from the computer-readable storage medium and executes the executable instructions, it implements the rapid simulation method for transient waveforms of typical faults in offshore wind power as described in any one of claims 1-2.

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